When communicating data blocks between transmitting and receiving devices in a communication system over a wireless interface, typically some type of error detection and error correction mechanism is used to assist in the decoding of each data block at the receiving device for enabling further processing of the data block. Herein, a data block is generally defined as a block of continuous bits containing information and/or signaling, and decoding is defined as the initial processing of a received data block to identify the received bits (e.g., as 1s or 0s) and may include, detecting and/or correcting errors in the received bits. Signaling is concerned with the establishment and control of connections in a network.
Generally, a data block has a predetermined logical structure having a plurality of different types of fields for organizing the bits in the data block, and one or more or these fields may contain bits that enable the error detection and/or error correction for that field. However, depending on the protocol used, some fields may include error correction bits but not error detection bits or limited error detection bits because of a bit number constraint due to, for instance, bandwidth constraints associated with the physical channels over which the data block is sent. A resulting limitation is that an inability to detect decoding errors in some fields can cause fairly substantial problems related to the further processing of the data block if there are, in fact, errors that go undetected.
An example of an air interface protocol that has a data block structure that includes fields having error correction but not error detection is the air interface protocol defined in accordance with the ETSI (European Telecommunications Standards Institute) TS (Technical Specification) 102 361-1. A data block structure identified in this technical specification is a burst, which is defined as the smallest predefined block of continuous bits containing information or signaling. More particularly described therein is a DMR (Digital Mobile Radio) TDMA (Time Division Multiple Access) burst. The DMR TDMA burst includes, for instance, a Data Type field that identifies the type of data being transmitted in an Information field, which is also included in the burst. There are a number of data types mentioned in the technical specification including, e.g., Voice LC Header, Terminator with LC, CSBK, Data Header, etc. Since this field is subject to error correction (in this case forward error correction (FEC), which is well known in the art) but not error detection, it is not possible for a receiver to know whether the error correction on the Data Type field was successful. Because of this, it may be possible under certain error conditions for some burst types to be processed incorrectly.
For illustrative purposes, following are two examples of problems that may arise due to a failure to detect an incorrectly identified data type. In one example, a CSBK could mistakenly be interpreted as a Data Header (which is a first burst of a multi-burst data message), due to uncorrectable errors on the channel. Since a Data Header contains a Blocks to Follow field specifying how many additional bursts belong to this transmission and a CSBK does not, the receiver treats the subsequent bursts as part of that data transmission. Accordingly, other transmissions, such as new voice transmissions, CSBKs, and new data transmissions, are missed during this period.
As another example, a Terminator with LC could mistakenly be interpreted as a Voice LC Header. As many Terminator with LC bursts are typically transmitted during Call Hangtime, the potential side effects include causing a receiver to begin processing a new voice transmission when none exists.
Therefore, it is desirable to have a method and apparatus to provide reliable error detection for a field without or with limited bits reserved for error detection.